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before going to the sleep -in between sleep and consciousness- sometimes i feel like i am pushed towards my chest and my chest sucks me in very fast..it feels like such a shock..i almost jump slightly in the bed as i lay still ..it happens only in haldf of a second..and then i forget that..i suspect that it is a natural thing that it happens every night but i notice it only when i am physically very very  tired . any ideas?

I get that often too, but at the other end.  That is, as I'm waking back up after sleep and always after dreaming.
My thoughts on that are that it was more than a dream, that I was "out there" and felt the return.  Not sure about at the beginning..